In Wavelength Division Multiplexing (WDM) optical communications networks, optical signals are transmitted at predetermined wavelengths in which each wavelength forms a communication channel in the network and the wavelength of the optical signal is used to control the destination of the signal through the network. In Dense Wavelength Division Multiplexing (DWDM) networks, the number of wavelength channels is increased by reducing the channel wavelength separation. In a standard DWDM network, the separation between communication channels is 100 GHz, and 50 GHz in more advanced systems.
In WDM and DWDM networks, switches are used to select paths for optical signals through the optical fibers forming the networks, i.e., to direct optical signals from one optical fiber to another and from one wavelength channel to another. Switches tend to be large and complex, interconnecting many inputs and outputs over multiple wavelengths.
One type of switch implementation, such as arrayed waveguide grating (AWG) implementations, entails complicated routing and wavelength sequencing. Moreover, for AWG implementations with large numbers of inputs and outputs, it is not clear that such implementations are truly reconfigurable on any wavelength and between any input and any output.